The effect of Nb addition on the precipitation and precipitate coarsening behavior was investigated in Ti and Ti + Nb steel weld HAZ. A dilatometer equipped with a He-quenching system was used to simulate the weld thermal cycle. Compared to $TiC_yN_{1-y}$ precipitate in a Ti containing steel, $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle with addition of Nb is precipitated in a Ti + Nb containing steel. Meanwhile, precipitate coarsening occurred more easily in Ti + Nb steel, which may be because the high temperature stability of $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle is deteriorated by the Nb addition.